A hexagon has 6 sides, all equal to one another, which means it has symmetry. Simply fold the hexagon until it makes a triangle
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Put one angle of each triangle at the center of the hexagon.
Join them together
First make a regular hexagon. Then take any one triangle and slide it through two heights so that it's base is on what was the opposite side. You will have an irregular, concave hexagon, shaped somewhat like an arrowhead.
Only an equilateral triangle, square and a regular hexagon can be used to make regular tessellations but there are innumerable polygonal and non-polygonal shapes which will tessellate by themselves, and others which will tessellate along with other shapes.
You Cant. Because A Hexagon Is A Six Sided Shape. And An Equilateral Triangle Is Equal. So You Can Because Everything (As In Sides And Angles Will Be Congruent)